This invention generally relates to an apparatus for holding wafers during process steps used in the manufacture of semiconductor devices and more specifically to such apparatus for use in such manufacturing processes wherein a hot gas stream is used for treating the wafers.
This invention describes improvements to a non-contact substrate holding device using a gas vortex principle for processing substrates and particularly for manufacture of micro-pattern devices. The terms substrate and wafer are used herein interchangeably to depict the object being handled in processes leading to a semiconductor device.
Production of devices employing micron and sub-micron sized micro-patterns require fabrication of the devices on much larger substrates before dicing the substrates or wafers into the individual devices or xe2x80x9cchips.xe2x80x9d Process steps to form micro-patterns in large substrates are the bases for manufacturing micro-electronic devices, such as logic and memory chips, and Miniature, Electronic-Mechanical Machined Devices (MIMMS), such as miniaturized gas, pressure and strain sensors.
A preferred substrate or wafer processing technique for which the invention can be used involves the treatment of a wafer by an intense hot gas stream. Hot gas process applications include etching material from the substrate and thermal processing of the substrate. One such an application is described in a U.S. Provisional patent application Serial No. 60/156,407, filed Sep. 28, 1999 and entitled xe2x80x9cAtmospheric Process and System For Controlled Rapid Removal of Polymers From High Depth to Width Aspect Ratio Holesxe2x80x9d.
The principle of holding a wafer in a non-contacting manner with a vortex holding scheme is described in detail in the international patent WO9745862, entitled xe2x80x9cNon-contact holder for wafer-like articles,xe2x80x9d inventors Siniaguine and Steinberg, filed 1997. A schematic presentation of a prior art non-contact vortex type substrate holder as described by WO9745862 is shown in FIG. 1 in this application.
Use of a holder using a gas vortex principle for the non-contact transport of heavy articles has been described in patent SU537924 (Soviet Union), entitled xe2x80x9cVacuum lifting device,xe2x80x9d assignee Khark Aviation Institute, filed 1977. Atmospheric plasma systems for processing substrates that use a non-contact substrate holder based on a gas vortex principle have been described in the international patents WO9621943, entitled xe2x80x9cDevice for treating planar elements with a plasma jet,xe2x80x9d Mikhailovich et al, filed 1995; and WO9221220, entitled xe2x80x9cApparatus for the treatment of a solid body,xe2x80x9d Vecleslav et al, filed 1992. Specific hardware designs for a vortex chuck substrate holders are described in international patents WO9946805, entitled xe2x80x9cHolders suitable to hold articles during processing and article processing method,xe2x80x9d Kaufman and Siniaguine, filed 1999; and WO6095582 entitled xe2x80x9cArticle holders and holding methods,xe2x80x9d John and Siniaguine, filed 1999.
When a hot gas stream, that is smaller in cross-section than that of the substrate, is used to treat the substrate, the substrate holder must move the substrate through the hot gas treatment area with a controlled motion pattern so as to uniformly treat the substrate. Use of a non-contact vortex type substrate holder for processing substrates with a hot gas stream generated by an atmospheric arc type plasma, often referred to as a plasma jet, is described in WO9745862, WO9621943, WO9221220 and WO9946805, referenced above. The motion configurations described in these patents relate to processing batches of substrates using multiple holders. Heat is transferred from the substrate to the holder and presumably from the holder to the ambient gas inside the process chamber.
An atmospheric plasma generating system, often referred to as a plasma jet that can be used to generate a suitable hot gas stream, has previously been described, see U.S. Pat. No. 6,040,548, by Siniaguine, entitled xe2x80x9cApparatus for generating and deflecting a plasma jet,xe2x80x9d filed 1997.
In the above prior art, wherein use of vortex type substrate holders is described, wafers are processed in batches and heat is transferred to the substrate holder from the substrate by air cooling that is enhanced by the holders"" motion. Conventional vortex type non-contact substrate holders nevertheless, have the following disadvantages:
1. Heat transfer from the substrate to the holder is a function of gas flow along the substrate surface inside a gap between the substrate holder and the substrate. The gas flow is produced by a rotating gas, which emerges from the vortex chucks. This gas flow is not uniform over the surface of the substrate facing the wafer holder and as a result uneven temperatures across the wafer during processing tend to arise.
2. With accelerating motions of the substrate holder the substrate can impact the xe2x80x9climitersxe2x80x9d that constrain the wafer to the holder. For mechanically delicate substrates, this impact can chip the substrate edges.
3. Edge effects tend to arise in processes using a hot gas stream. When the substrate is moved out of the gas stream, the gas flow characteristics are different near the edge of the substrate compared to when the gas stream is near the substrate center. This can cause non-uniformity in the processing that may be difficult to compensate for by varying process parameters.
4. The ability to handle high heat flux is limited. Hence when processing applications require a high heat flux onto the substrate surface, very rapid heat removal from the substrate to the holder and from the holder may be required to avoid an uncontrolled upward drift in the wafer temperature during processing.
Compared to substrate holders that mechanically clamp the substrate against a cooled surface for heat removal, such as by electrostatic clamping or vacuum clamping, a non-contact wafer holder is particularly useful for applications that involve processing with an intense hot gas stream whose treatment area is smaller than the substrate size. Differential heating of the wafer due to the localized area of the treatment area can cause temporary thermal distortion of the wafer. A non-contact holder can allow the wafer to move without putting mechanical stress in the wafer from mechanical constraint and at the same time not strongly affecting the local heat removal capability.
In one method and apparatus in accordance with the invention, the wafer, which is being processed, is held by a vortex-type substrate holder against a moveable frame. Motion of the wafer is controlled with movement of the frame. The frame can be shaped to provide a sealed chamber through which gas used to create the vortices is re-captured. With such sealed chamber a higher heat conducting but more expensive gas can be re-cycled and used for the vortex holder and cooling of the wafer.
In another technique of this invention, damage of the wafer edges from impacts with position limiters is avoided by inserting a small physical off-set of the center of mass of the wafer relative to that of the frame used to rotate the wafer. This prevents sliding of the wafer within the holder.
In another feature of the invention end effects during treatment of the wafer are avoided by providing an extension around the wafer. The extension assures that the treating gas stream provides the same treatment to the edge of the wafer as in its center.
It is, therefore, an object of the invention to provide improved more uniform treatment of substrates, better temperature control of the substrates, and less possibility of damage to substrate edges.
It is a further object of this invention to provide methods to improve the performance of a vortex chuck retention mechanism during the processing of a wafer with an intense hot gas stream that is smaller in size than the wafer.
It is a further object of the invention to provide a method and apparatus with which temperature imbalance effects on the wafer from the vortices used to hold the wafer are reduced, with which the need for a rotating gas seal is advantageously eliminated to avoid the generation of incompatible particles and with which a chipping of the substrate edges from impact of the substrate against holder limiters during accelerations of the substrate holder is avoided.
It is still further an object of the invention to provide a wafer holder that enables similar gas flow conditions for the hot gas stream treatment area near the outer edge compared to the central area of the substrate. This allows for more uniform treatment of the substrate. The programmed motion of the substrate through the hot gas stream treatment area then more easily compensates for treatment effects near the edge of the substrate.
With a substrate holder in accordance with the invention the treatment of a substrate by a hot gas stream can be done with tight control of the substrate temperature and with an increase in the heat transfer from the substrate. A direct fluid cooling of the substrate holder can be done with process temperature feedback to the cooling fluid temperature. Helium can be used as the gas injected into the vortex chucks of the substrate holder to yield significantly higher heat conductivity while enabling a re-circulation of the helium to reduce expenses. Variations in the local heat removal from the substrate can be obtained by injecting gas into the vortex chucks that has the same temperature as the substrate holder. A greater heat removal from the substrate is made possible with tight control of temperature by using a liquid, such as water, and use its heat of vaporization for cooling of the substrate.
With a motion configuration in accordance with the invention a rotary motion is combined with translation for the substrate through a treatment area in an advantageous manner for full treatment of a substrate by a smaller treatment area. Since gas flow for the vortex substrate holder to a conventional rotating substrate holder must go through a rotating gas seal, the rotating seal tends to generate some microscopic particles that can cause a yield problem in the manufacture of devices especially when these have feature sizes in the micron and sub-micron range. With one substrate holder in accordance with the invention the vortex holder is separated from the rotating mechanism so that a rotating gas seal is not necessary and, therefore, small particles from the seal are not produced.
These and other advantages and objects of the invention can be understood from the following detailed description of the drawings in which: